Thanks for your question Robert. Hub pages currently inherit the header settings for the site they belong to. If you would like a different header it would need to be configured in the site editor and would apply to all pages that belong to that site. See this blog post for best practices:https://community.esri.com/community/gis/web-gis/arcgis-hub/blog/2016/10/11/beta-sites-custom-header....
Re the sign in link, this should be considered a core feature for all Hub sites and pages and cannot be removed. Visitors to your site can favorite certain datasets and gain access to their download history when signed in. Additionally, if you have non-public content, you can grant access to users in your organization presented alongside public content by allowing users to sign in. If you're only using the webpage builder part of the product then a sign in link might seem unnecessary. That said, opening up sites and pages to the ArcGIS named user community is central to the larger Hub product vision and there are currently no plans to remove in the future.
